Modular prosthesis and use thereof for replacing a radial head

ABSTRACT

A modular prosthesis system for replacement of a head portion of a proximal radius includes a monolithic stem component, a head component, and a locking mechanism formed by the stem and head components. The stem component defines a stem anchoring portion having a longitudinal axis and configured to couple to the proximal radius, and a dovetail-shaped first mounting portion on a first end face that extends in a first direction transverse to the longitudinal axis. The head component has a dovetail-shaped second mounting portion on a second end face opposite the first end face slidably engaged with the first mounting portion along the first direction. One of the first and second mounting portions intersects the longitudinal axis. The locking mechanism is formed at an interface between the stem and head components and is engaged through relative translational movement between the stem and head components. A related method is provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/999,297, filed on Nov. 29, 2004, which is a continuation-in-part ofU.S. patent application Ser. No. 10/464,043, filed Jun. 18, 2003 (nowabandoned), which is a continuation of Ser. No. 09/828,745, filed Apr.9, 2001 now issued as U.S. Pat. No. 6,656,225 B2 on Dec. 2, 2003, whichclaims the benefit of U.S. Provisional Application No. 60/195,444, filedon Apr. 10, 2000. The disclosures of the above applications and patentsare hereby incorporated by reference as fully set forth herein.

FIELD

The present invention relates to prostheses for the elbow joint, andmore specifically to prostheses for replacing a proximal head of theradius.

BACKGROUND

Trauma to the elbow joint frequently involves damage to the ligamentoussupport of the elbow and fractures of the osseous structures responsiblefor the skeletal integrity of the elbow joint. The proximal aspect ofthe radius, or radial head, is frequently injured either in isolation orin combination with injury to other bony or ligamentous structures ofthe elbow joint. The radial head may also be fractured in associationwith injuries to the forearm axis, including disruptions of theinterosseous membrane between the radius and the ulna. Whether inisolation or in combination with other injuries, fractures of the radialhead can be difficult to treat.

Fractures of the radial head are either reconstructable orunreconstructable. Despite various technical advances in thereconstruction of radial head fractures, a certain percentage offractures are not amenable to reconstruction due to the degreecomminution or severity of the fracture. In general, unreconstructableradial head fractures result from high energy trauma and are thereforefrequently associated with significant injuries to other osseous orligamentous structures of the elbow joint or forearm. In these cases,restoration of the stabilizing function of the radial head is criticalto allow the ligaments of the elbow or forearm to heal in appropriaterelationships, thereby restoring stability to the elbow or forearm. Thisstabilizing function depends, in part, upon re-establishing theappropriate distance between the capitellum and the proximal shaft ofthe radius.

Prosthetic replacement of the radial head has evolved rather slowly. Thefirst widely used prosthetic radial head was introduced in the 1970'sand was composed of silicone. Silicone implants placed in various jointsthroughout the body led to “silicone synovitis,” in which the siliconeinduced an inflammatory response within the joint. Further, siliconeradial head prostheses were found to be incapable of resisting thestresses to which the radial head is subjected, rendering it less usefulin stabilizing the injured elbow or forearm.

The difficulties apparent with silicone led to experimentation withmetal radial head implants. These prostheses are fashioned from a singlepiece of metal (often titanium) and include a stem and a head portion.The head portion is shaped to approximate the anatomy of the radialhead. These metallic prostheses are capable of resisting the compressivestresses to which the radial head is subjected, as has been demonstratedin several biomechanical studies. However, significant problems remainwith these prostheses.

Anatomic and radiographic studies of the dimensions of the radial headreveal a disparity with currently available metallic prostheses.Therefore it has been difficult to restore appropriate anatomicalignments within the elbow. Therefore restoration of the appropriaterelationship between the capitellum and proximal shaft of the radius hasbeen very difficult to achieve with these prostheses. Additionally, thefact that these prostheses are fashioned from a single piece of metalhas led to technical difficulties with insertion and removal. Surgeonshave had difficulty with matching both the size of the stem to the canalof the proximal radius and the size of the head portion to the patient'snative radial head. Removal of these non-modular components frequentlyrequires release of the lateral ligaments of the elbow and the annularligament, which binds the neck of the proximal radius to the proximalulna. Thus the elbow is frequently destabilized during removal of theseprostheses.

Designers of prosthetic joint replacements in the hip, shoulder, kneeand fingers have circumvented the above mentioned difficulties byemploying the use of modular components. Modularity allows for eachaspect of a prosthesis to be sized appropriately to its recipientanatomic site. The concept of modularity has only recently been appliedto commercially available radial head prostheses. Currently availablemodular radial head prostheses employ a mechanism by which the headcomponent is impacted over and onto the stem component. The surgicalexposure must therefore allow sufficient room for the head to bemaneuvered over the stem prior to being impacted. With impaction, theheight of the prostheses may be decreased, resulting in an increaseddistance between the capitellum and the proximal end of the radius.Increasing this distance alters the bony anatomy such that the ligamentsof the elbow joint are not held in their appropriate lengths andtensions. Instability of the elbow or inappropriate healing of theligaments may result. Furthermore, removal of these prostheses isaccomplished in the same manner as the above mentioned metallicimplants, often requiring destabilization of the lateral aspect of theelbow joint.

In order to reap the benefits of modularity in radial head prostheticreplacement, a reliable and surgically appropriate method to secure thestem of the prostheses to the head of the prostheses and which allowsfor accurate restoration of the appropriate spatial relationshipsbetween the bones of the elbow is required.

SUMMARY

A modular prosthesis system for replacement of a head portion of aproximal radius includes a monolithic stem component, a head component,and a locking mechanism formed by the stem component and the headcomponent. The stem component defines a stem anchoring portion having alongitudinal axis and configured to couple to the proximal radius, and adovetail-shaped first mounting portion on a first end face that extendsin a first direction transverse to the longitudinal axis. The headcomponent has a dovetail-shaped second mounting portion on a second endface opposite the first end face slidably engaged with the firstmounting portion along the first direction. One of the first and secondmounting portions intersects the longitudinal axis. The lockingmechanism is formed at an interface between the stem component and thehead component and is engaged through relative translational movementbetween the stem component and the head component along the firstdirection.

A method of use for a modular prosthesis for replacement of a headportion of a proximal radius includes coupling a stem anchoring portionof a monolithic stem component having a longitudinal axis to a resectedportion of the proximal radius, and coupling a dovetail-shaped firstmounting portion on a first end face of a head component that extends ina first direction transverse to the longitudinal axis to adovetail-shaped second mounting portion on a second end face of the stemcomponent that extends in the first direction. The coupling the firstmounting portion includes slidably engaging the first mounting portionwith the second mounting portion by moving the head component in thefirst direction, and connecting the head component and the stemcomponent by moving the head component in the first direction after theslidably engaging until a locking mechanism formed by the stem componentand the head component at an interface is engaged, wherein one of thefirst and second mounting portions intersects the longitudinal axis.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a front view of a stem component;

FIG. 2 is a side view of the stem component from a perspectiveperpendicular to that of FIG. 1;

FIG. 3 is a top view of the stem component;

FIG. 4 is a front view of an inner core of a head component;

FIG. 5 is a side view of the inner core of the head component from aperspective perpendicular to that of FIG. 4;

FIG. 6 is a top view of the inner core of the head component;

FIG. 7 is a front view of an outer shell of the head component;

FIG. 8 is a side view of an outer shell of a head component from aperspective perpendicular to that of FIG. 7;

FIG. 9 is an exploded perspective view of an assembly of a stemcomponent, a inner core, and an outer shell;

FIG. 10 is a perspective view of an assembled prostheses;

FIG. 11 is a front view of an assembled prostheses;

FIG. 12 is a side view of an assembled prostheses from a perspectiveperpendicular to that of FIG. 11;

FIG. 13 is a top view of an assembled prostheses;

FIG. 14 is a posterior oblique view of a human elbow depicting a radialhead prostheses in position within a proximal radius bone andarticulating with a capitellum of a distal humerus;

FIGS. 15 and 16 are perspective views of a tool that can be used toinsert or remove a head component from a stem component via atranslational force;

FIG. 17 is a perspective view of the head component showing the outershell body completely enveloping the inner core

FIG. 18 is similar to FIG. 17 but shows the head component disassembled;

FIG. 19A is a perspective view of the head component showing the innercore extending beneath the outer shell body;

FIG. 19B is similar to FIG. 19A but shows a mechanical fastener securingthe outer shell body to the inner core;

FIG. 19C is similar to FIG. 19A but shows the head components as asingle piece;

FIG. 20 is similar to FIG. 19 but shows the head component disassembled;

FIG. 21A is a perspective view of the head component, the stem componentand a collar component;

FIG. 21B is similar to FIG. 21A but shows an alternative configurationbetween the head component, the stem component and the collar component;

FIG. 22 is similar to FIG. 21A but the components are assembled;

FIG. 23 are perspective views of exemplary alternative connectionsbetween components of the modular prosthesis;

FIG. 24 is similar to FIG. 21A but shows an angled collar component;

FIG. 25 is similar to FIG. 24 but the components are assembled;

FIGS. 26A-26D are perspective views of exemplary alternative connectionsbetween the head component, the stem component and the collar component;and

FIG. 27 is perspective view of a kit including a plurality of headcomponents, stem components and collar components having various sizes,shapes and configurations.

DETAILED DESCRIPTION OF THE VARIOUS EMBODIMENTS

The following description of the preferred embodiment(s) is merelyexemplary in nature and is in no way intended to limit the invention,its application or uses.

Before the present invention is disclosed and described, it is to beunderstood that this invention is not limited to the particularconfigurations, process steps and materials disclosed herein as thesemay vary to some degree. It is also to be understood that theterminology used herein is used for the purpose of describing particularembodiments only, and is not intended to be limiting as the scope of thepresent invention. The invention will be limited only by the appendedclaims and equivalents thereof.

It must be noted that, as used in this specification and the appendedclaims, singular forms of “a,” “an,” and “the” include plural referentsunless the content clearly dictates otherwise.

“Radial head” is defined as the essentially cylindrical protrusion foundat the proximal end of a radius bone. The term “radial head” can also beused to modify or describe the prostheses of the present invention.

“Longitudinal axis” is an imaginary line that is defined by the centerof the stem component in the direction of intramedullary canalinsertion. Thus, the “longitudinal axis” is also roughly defined asrunning parallel to a centerline running between the proximal and distalend of the radius bone.

“Transverse axis” or “assembly axis” is an axis that intersects thelongitudinal axis. The transverse axis can be linear or non-linear. Forexample, if non-linear, the axis can be arcuate, provided the assemblyaxis intersects the longitudinal axis. Thus, angles >0° and <180°qualify as “transverse.” However, for practical purposes, the transverseaxis can be from 45° to 135° with respect to the longitudinal axis inorder to significantly benefit from the modular assembly benefitsdescribed herein. In many instances, an essentially perpendiculartransverse axis with respect to the longitudinal axis will be present.

“Protuberance” can include any protuberance functional with the presentinvention, particularly with respect to certain locking mechanisms. Forexample, such protuberances can be convexities.

“Concavity” is intended to describe an open space defined by a mountingportion of a stem component, or an inner core. With respect to a lockingmechanism, the concavity can be configured to inversely match and accepta protuberance, though this is not required.

“Intramedullary” shall mean the within the marrow cavity of a bone.

“Native” is used to describe the condition of the bone or the head of abone prior to damage or removal.

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the exemplary embodimentsillustrated in the drawings, and specific language will be used todescribe the same. It will nevertheless be understood that no limitationof the scope of the invention is thereby intended. Any alterations andfurther modifications of the inventive features illustrated herein, andany additional applications of the principles of the invention asillustrated herein, which would occur to one skilled in the relevant artand having possession of this disclosure, are to be considered withinthe scope of the invention.

In order to remedy the shortcomings of prosthetic radial headreplacement, a radial head prosthesis is disclosed that enables theassembly without having to significantly remove or manipulate bone andtissue as part of an overhead assembly. By implementing a slidingmechanism for the assembly of the modular radial head prostheses asdescribed herein, improvement over the commercially availableprosthetics can be achieved. Specifically, a sliding mechanism inconjunction with a locking mechanism enables the secure attachment andreasonable removal of a head component from an intact stem component,without the disadvantages associated with head component insertion alongthe longitudinal axis.

With the above descriptions and definitions in mind, a stem component 10is shown in FIG. 1. Generally, the stem component 10 comprises ananchoring portion 12 and a mounting portion 14. The anchoring portion 12is the portion that is anchored within a canal of the proximal radius,providing support to the radial head prosthetic as a whole. In thisembodiment, the anchoring portion 12 is tapered and can be coated ortextured to allow bone ingrowth after insertion into the radius bone ofa patient. The anchoring portion can be cemented, press fit, and/orimpacted into the intramedullary canal as is known by those skilled inthe art. If a cement is used, then a cement such as, for example, methylmethacrylate, can be used. If desired, various sized broaches (notshown) can be provided such that the surgeon can sound the diameter ofthe proximal radial shaft, thereby selecting an appropriate sized stemcomponent. In this embodiment, the mounting portion 14 is configured asa dovetail shaped mount when viewed from the front perspective shown inFIG. 1. On each side of the mounting portion 14 are the stemprotuberances 16 a, 16 b. Though not required, the entire stem component10 (i.e., the anchoring portion 12, the mounting portion 14, and thestem protuberances 16 a, 16 b) can be constructed of a rigid materialsuch as metal, alloy, or ceramic. If the rigid material is metal oralloy, appropriate materials can include, for example, titanium,stainless steel, and cobalt chrome.

Turning to FIG. 2, a side view of the stem component 10 shown. As can beseen, the stem protuberances 16 a are configured to span a distance ofapproximately one half of the depth of the mounting portion. The stemprotuberance 16 b (not shown) is configured similarly. In FIG. 3, a topview of the stem component 10 is shown. As the mounting portion 14 isconfigured in a dovetail-type shape, the stem protuberances 16 a, 16 bare not visible from this perspective, and thus, are shown as dashedlines.

The stem component shown in FIGS. 1-3 has the dual purpose of attachingthe prostheses to the radius bone, as well as to provide a mechanism tomount a head component (not shown) to the stem component. Though thehead component can be a single unit, in the embodiment shown in thesubsequent figures, the head component comprises an outer shell and aninner core. The practical reason for this is that it is often desirableto have a rigid outer shell, while having a less rigid inner core whenutilizing the locking mechanism described in FIGS. 1-13. However, if thelocking mechanism does not utilize compressible protuberances as part ofthe locking mechanism, the inner core can be a rigid material as well.FIGS. 3-6 show an embodiment of the inner core, and FIGS. 7-8 show anembodiment of the outer shell. However, the inner core and the outershell will generally be pre-assembled prior to surgery.

Turning specifically to FIG. 4, an inner core 20 of a head component isshown. An inner core body 22 defines the shape of the inner core 20 andcan be constructed of a polymeric resin, such as, for example, a highmolecular weight polyethylene. Additionally, the outer dimension of theinner core body 22 can be cylindrical in shape. Attached to the innercore body are a pair of inner core protuberances 24 a, 24 b. The innercore body 22 and the inner core protuberances 24 a, 24 b define an innercore open channel or groove 26 that can be slidably connected to themounting portion (not shown) of the stem component (not shown). Theinner core protuberances 24 a, 24 b can be constructed of the samematerial as the inner core body 22, though this is not required. Thus,the inner core body 22 and the inner core protuberances 24 a, 24 b canbe a single polymeric or copolymeric unit. Whatever the structure, inthis embodiment, the inner core protuberances 24 a, 24 b are constructedof a compressible material so that the inner core protuberances 24 a, 24b can pass by the stem protuberances (not shown) as part of a lockingmechanism.

As can be seen more clearly in FIGS. 5 and 6, the inner coreprotuberances 24 a, 24 b are configured such that they span only aportion of the depth of the open channel 26. Thus, the inner coreprotuberances 24 a, 24 b are positioned opposite the stem protuberances(not shown) such that when the head component is in place on the stemcomponent, all of the protuberances act together to form a lockingmechanism.

As shown in this embodiment, the inner core open channel 26 does nottraverse completely through the inner core body 22. Thus, the inner coregroove 26 is just long enough such that when the mounting portion of thestem component (not shown) is tracked within the inner core open channel26, the mounting portion and the inner core 20 will be coaxial.

In FIGS. 7 and 8, a radial head component 30 is shown. An outer shellbody 32 is fashioned to approximate the dimensions of a damaged orremoved radial head. Thus, the outer dimension is roughly cylindrical,having a slightly concaved top portion 37 for natural articulation withthe capitellum (not shown). Because outer shell body 32 is the portionof the prostheses that will articulate with the capitellum upon jointmovement, this structure can be constructed of a biologically acceptablerigid material. Such a material can include, for example, metal, alloy,or ceramic. If the rigid material is metal or alloy, appropriatematerials can include, for example, titanium, stainless steel, andcobalt chrome. The outer shell body 32 also defines an inner hollow 34that accepts the inner core (not shown) when the head component is fullyconstructed. Additionally, an outer shell open channel or groove 36 ispresent that essentially matches the inner core open channel or groove(not shown) such that the mounting portion (not shown) can be insertedinto the aligned grooves. For example, the outer shell body 32 and theinner core (not shown) can both be cylindrical components that definedovetail shaped grooves, which substantially fits the dovetail shapedmount of the stem component. If the inner core 20 and the outer shellbody 32 are two different materials (as in the present embodiment), thenthe two components can be fitted together with a bonding cement,friction fit, and/or other known techniques. The outer shell openchannel or groove 36 can be present at only one edge of the outer shellbody 32 and its edges can be tapered to avoid damage to the articularcartilage of the proximal radio-ulnar joint. As mentioned, the outershell body 32 should be composed of metal suitable for biologicimplantation, and be shaped to approximate the dimensions of the radialhead. If the surgeon requires assistance in selecting an appropriatelysized head component, then an estimate of the patient's anatomy can beascertained using plastic trials (not shown) provided for this purpose.Though not required, the edges of the outer shell groove 36 can betapered to avoid damage to the proximal radio-ulnar joint.

Turning to FIG. 9, an exploded view of an embodiment of the presentinvention is shown. Specifically, the radial head component 30 is shownhaving an outer shell body 32, which defines an outer shell hollow 34.The outer shell hollow 34 fits over an outer dimension of the inner corebody 22 of the inner core 20. Once the outer shell body 32 and the innercore 20 are fitted together such that the outer shell open channel 36aligns with the inner core open channel 26, the entire head component(which comprises these two components) can be fitted on the mountingportion 14 of the stem component 10. Though not required, the lockingmechanism can be at an interface between the mounting portion 14 and theinner core 20. As shown in this figure, a pair of the stem protuberances16 a, 16 b can pass over a pair of the inner core protuberances 24 a, 24b, as the inner core protuberances 24 a, 24 b are configured tocompress. Once the stem protuberances 16 a, 16 b completely pass overthe inner core protuberances 24 a, 24 b, the stem protuberances can lockinto a pair of inner core concavities 25 a, 25 b, respectively. Theinner core concavities 25 a, 25 b are configured in dimension toinversely match the stem protuberances 16 a, 16 b such that a lockingaction occurs. Thus, an abutment of the protuberances occurs and canprevent unwanted motion between the head component and the stemcomponent after the prostheses is inserted. The protuberances also serveto prevent the head component from slipping off the stem componentwithout intentional force, e.g., during removal by a surgeon. With thisand other similar designs, the stem component can be placed in a canalof the radius bone, followed by the fitting of the head component.

FIG. 10 shows the stem component, the inner core 20 and the outer shellbody 32 in a completed assembly configuration. As can be seen, thecylindrical inner core 20 component fits centrally within the outershell body 32. Thus, when the mounting portion 14 of the stem component10 is inserted fully within the core and shell, all three componentswill be configured coaxially. Though the outer shell body 32 and theinner core 20 are shown as two separate components, in practice, theouter shell body 32 and the inner core 20 can be assembled andsterilized prior to attachment to the mounting portion 14 of the stemcomponent 10. Thus, the surgeon would only be required to slide theassembled head component onto the stem component 10 by lining up theopen channels 26, 36 with the mounting portion 14, and sliding theradial head component 30 into place. In FIGS. 11-13, additional views ofan assembled prosthesis are shown.

When assembling the head component onto the mounting portion 14, due toelastic deformation of the inner core protuberances 24 a, 24 b, all ofthe protuberances 16 a, 16 b, 24 a, 24 b can be slid past opposingprotuberances under sufficient translational force. In this embodiment,the protuberances are shaped such that the force required to press theprotuberances past their opposing protuberances is intentional andreasonable, but not excessive.

FIG. 14 is a posterior oblique view of the human elbow depicting theradial head prostheses in position within the proximal radius bone 38and articulating with the capitellum 39 of the distal humerus. As can beseen, the anchoring portion 12 is within the medullary canal of theproximal radius 38, and the radial head 30 is articulating with thecapitellum 39 of the distal humerus.

In FIGS. 15 and 16, a tool 40 is shown that can be used with theprostheses of the present invention is shown. In FIG. 15, the tool 40 ispositioned in a first orientation with respect to proximal radius 38 forinserting the radial head component 30 onto the mounting portion 14. InFIG. 15, the tool 40 is positioned in a second orientation with respectto the proximal radius 38 for removing the radial head component 30 fromthe mounting portion.

Specifically, with respect to FIG. 15, a first arm 42 and a second arm44 are shown that enable or surgeon to create translational force 45 tobe placed on the radial head component 30. The first arm 42 and thesecond arm 44 are tracked parallel to one another by a track 46 and aslider 48. The second arm 44 is connected to a handle 52 by a hinge 50.The handle 52 is designed such that by applying a squeezing force 51,translational force 45 is applied to the head component 30. Thus, inthis embodiment, the translational force mechanism is a lever. At theend of the first arm 42 is a pulling member 54 that acts to stabilizethe proximal radius 38 (or alternatively, the mounting portion 14). Atthe end of the second arm 44 is a pushing member 56 for pushing theradial head component 30 onto the mounting portion 14.

In FIG. 16, the same tool 40 as described in FIG. 15 can be used byflipping it upside down. Thus, the first arm 42 now acts to provide thetranslational force 45 and the second arm 44 stabilizes the proximalradius 38 (or alternatively, the mounting portion 14). Thus, the armsare characterized as the first arm 42 and the second arm 44 forconvenience only. It would be apparent to one skilled in the art thatthe first arm or the second arm can function as the stabilizer.Likewise, the first arm or the second arm can act to provide desiredtranslational force.

The use of such a tool is particularly helpful when a locking mechanismsuch as that described in FIGS. 1-13 is in place. Locking and unlockingcan be carried out as previously described. Specifically, in the presentembodiment, the tool can press the components onto one another whilemaintaining alignment of the dovetail shaped mount and groove. In theabsence of intentional and sufficient pressure to translate the headcomponent off of the stem component, the rigidity provided by thepolyethylene is sufficient to secure the modular components to eachother. Removal is accomplished by generating sufficient translationalpressure on the head component with the use of a specially designedhandle. This tool binds the far end of the head component whilestabilizing the proximal radius bone, and thereby the stem component.Translational force is generated which presses the protuberances of theinner core past the protuberances of the mounting portion, therebyreleasing the head component from the stem component.

A procedure that can be followed for the insertion of the modular radialhead prostheses is as follows. If necessary, after resection of asubstantially unreconstructable radial head bone, a proximal edge of theradius bone can be removed by transverse sawing or some other removaltechnique. After the damaged radial head has been removed, the medullarycanal of the bone can then be broached with one or more of a series ofbroaches, the shapes of which approximate the various stem sizesavailable. Once an appropriate size stem component size has beenselected, the anchoring portion can be inserted into the proximal radiusbone such that the mounting portion protrudes from the proximal radiusbone. The head component can then selected based upon parameters such asproper ligament tensioning, circumference, and height. If desired, thisassessment can be assisted with the use of plastic trials made availablefor this purpose. After an appropriately sized head component isselected, the forearm can be rotated so that the mounting portion ispositioned to receive the head portion, i.e., an assembled outershell/inner core combination or a single piece head component. If thehead component comprises an outer shell and an inner core, the headcomponent can either be assembled at the time of manufacture or by thesurgeon. In any event, the outer shell groove and the inner core grooveshould be position such that the grooves line up for accepting themounting portion. Once the stem component is in place and the properhead component is assembled and selected, the head component is thentranslated onto the stem component fully. If a locking mechanism is usedsuch as that described in FIGS. 1-13, a click will be palpable as thestem protuberances and the inner core protuberances slip fully past eachother. The prostheses will then be secure within the canal of theproximal radius bone and is positioned to articulate with the capitellumof the distal humerus.

With the above figures and surgical procedures in mind, a modularprostheses system for replacement of the radial head portion of theradius bone is disclosed comprising a stem component and a headcomponent. The stem component comprises an anchoring portion and amounting portion, and the head component can have an open channelconfigured to connect to the mounting portion along an assembly axisthat is transverse to a longitudinal axis of the stem component. Theconnection can be by a sliding motion. Though the system requires onlythat the assembly axis be transverse to the longitudinal axis of thestem component, for practical purposes, the transverse angle willgenerally be from about 45° to 135° with respect to the longitudinalaxis. This is due to the fact that as you approach angles closer toparallel with the longitudinal axis, the head component becomes moredifficult to put in place. In many incidences, the assembly axis willintersect the longitudinal axis at essentially a perpendicular angle.

The system can further comprise a locking mechanism to prevent the openchannel of the head component from indeliberately sliding on themounting portion once connected to the mounting portion. This isdesirable because once the prosthesis has become part of the functioningelbow joint, any slippage could require surgery for repair. Thus, theonly circumstance wherein sliding should be allowed should occur at thehand of the surgeon, with deliberate action. The locking mechanism canbe configures such as that shown in FIGS. 1-13, or by any other lockingmechanism known by those skilled in the mechanical arts. For example,after sliding the head component onto the mounting portion, the headcomponent can be locked in place with a pin or screw.

In a one embodiment, the mounting portion can be configured for allowingthe head component to slide along a single axis via the open channel.Such an embodiment is shown in FIGS. 1-13 where the dovetail-shapedmounting portion is inversely matched with a dovetailed-shaped groove.Thus, head component can be slid onto the mounting portion along asingle axis only.

Though not required, the head component can be inserted and removed fromthe mounting portion with a specially designed tool. Thus, the system ofthe present invention can further comprise a tool for inserting andremoving the head component while the stem component is in place withina radial canal. Such a tool can comprise a first arm for inserting thehead component onto the mounting portion or removing the head componentfrom the mounting portion; a second arm for stabilizing the radius bone;and a translational force mechanism for moving the first arm while thesecond arm stabilizes the radius bone. The terms “translation” and“stabilizing” are used loosely depending on whether the tool is beingused for insertion or removal of the head component, the arm acting toprovide the translational force and the arm act to provide stabilizationcan be changed. Thus, the terms are relative as to the action, ratherthan to the specific structure. For example, when insertion of the headcomponent is being carried out, the first arm carrying out thetranslational insertion does so by a pushing force, and the second armstabilizes the radius bone by a pulling force. Conversely, when removalof the head component is being carried out, the first arm removes thehead component by a pulling force (i.e., the tool is flipped over, andthe second arm stabilizes the radius bone by a pushing force).

As part of the system, a method for fitting a damaged radius bone with amodular radial head prostheses is disclosed comprising the steps ofsecuring a stem component partially within a proximal intramedullarycanal of the damaged radius bone such that a mounting portion of stemcomponent is exposed above the damaged radius bone; selecting a headcomponent that will provide a desired result; and sliding the headcomponent onto the mounting portion in a direction along an assemblyaxis that is transverse to a longitudinal axis of the stem component.Typically, a preliminary step of removing a radial head of the damagedradius bone is carried out prior to fitting the radius bone with theprostheses of the present invention, though there can be circumstanceswhere this preliminary step is not necessary. Additionally, beforesecuring the stem component within the intramedullary canal, it may bedesirable to carry out the preliminary step of sizing the stem componentto securely fit within the proximal canal. This can be done using a setof broaches designed for this purpose. The stem component can be securedwithin the intramedullary canal by one of a number of techniquesincluding the use of cement, firm pressure into the canal, or impactingthe stem component into the canal, for example.

Once the stem component is in place, the next step of selecting anappropriate head component is carried out. Considerations can includeassessing a desired tensioning of one or more ligaments attached to theradius bone and/or assessing the height and shape of the head componentto be used. Aid in this area can be provided by the use of trialsdesigned for this purpose. Such trials can be plastic structuresconfigured to approximate the size and shape of the head component to beultimately placed on the mounting portion. It is appreciated that thetrials can be made of other suitable materials.

Referring to FIGS. 17 through 20, the inner core 20 and the outer shellbody 32 of the radial head component 30 are shown. In the variousembodiments, the outer shell body 32 can be comprised of ultra highmolecular weight polyethylene. The outer shell body 32 can also becomprised of a suitable metal material such as cobalt chrome, titanium,or other biocompatible material. The inner core 20 can also be made of amaterial that is identical to the radial head component 30 (FIG. 19B) oras above described made of a softer material (FIG. 19A) that canotherwise be compressed when inserted over the stem protuberances 16 a,16 b or any other biocompatible material, as above detailed and as shownin FIG. 1.

In other embodiments, the inner core 20 and the outer shell body 32 arecomprised of the same material (FIG. 19B), for example, a metal such ascobalt chrome or titanium. By way of example, a mechanical fastener 60can be used to secure the outer shell body 32 to the inner core 20 inlieu of the compressible inner core protuberances 24 a, 24 b (FIG. 4).In addition, the head component 30 can be made of single piece ofbiocompatible material (FIG. 19C), such that the head component is aunitary construction. It is appreciated that a plurality of thefasteners 60 can be used to secure the outer shell body 32 to the innercore 20. Moreover, other types of exemplary connections may be used suchas chemical bonding, shrink fit and taper junctions. Furthermore, theouter shell body 32 can be configured to snap fit onto the inner core20, while another method can include mechanical threading on the innercore 20 with complementary mechanical threading on the outer shell body32. The outer body shell 32 of the radial head component 30 can also beconfigured to completely envelope the inner core 20, as shown in FIGS.17 and 18, or otherwise be positioned over the inner core 20 as to notcover the open channel 26 thus exposing varying lengths of the innercore 20, as shown in FIGS. 19A, 19B and 20.

With reference to FIGS. 21A through 24, a collar component 62 can beused to connect the radial head component 30 to the stem component 10.The collar component 62 can have a collar open channel 64 and a collarmounting location 66, which are complementary to the head open channel36 and the stem mounting location 14, respectively. The collar component62 can be configured to vertically align the radial head component 30and the stem component 10, as shown in FIG. 22. An angled collarcomponent 68 can also be configured to provide a pre-determined anglebetween the radial head component 30 and the stem component 10, as shownin FIG. 25. As such, the angled collar component 68 can be configured atvarious angles, for example, between vertical (i.e., 180°) and narrowerangles to match the native geometry of the bones, as shown in FIG. 14.It can be appreciated that the radial head component 30 and the stemcomponent 10 can attach to the collar component 62 or the angled collarcomponent 68 regardless of its length or angle.

In the various embodiments, the radial head component 30 can have aunitary construction (i.e., one-piece), thus omitting the inner core 20and outer shell body 32. In this arrangement, the radial head component30 can be constructed of metal such as cobalt chrome, titanium or anyother suitable biocompatible material for implementation into the humanbody. By way of example, the radial head component 30 can be secured toeither the stem mounting portion 14 or the collar mounting portion 66 ofthe collar component 62 with a suitable mechanical fastener 60.

With reference to FIGS. 21A and 21B, the head component 30 includes afirst connection portion 70 that connects to a second connection portion72 on the collar component 62. The collar component 62 also includes athird connection portion 74 that connects to a fourth connection portion76 on the stem component 10. It can be appreciated that the secondconnection portion 72 can be distal from the third connection portion 74and can be on opposite ends of the collar component 62. As shown in FIG.21A, the first connection portion 70 can be the open channel 26 on thehead component 30. The second connection portion can be the collarmounting portion 66. The third connection portion 76 can be the collaropen channel 64. The fourth connection portion 78 can be the mountingportion of 14 on the stem component 10. As shown in FIG. 21B, the firstconnection portion 70 can be a head component mounting portion 78. Thesecond connection portion can be the collar open channel 64. The thirdconnection portion 74 can be the collar mounting portion 66. The fourthconnection portion 76 can be a stem component open channel 80.

It can be appreciated that the various components of the modularprosthesis system can use various connection portions with myriadconfigurations. By way of example, the mounting portion on the variouscomponents is configured in a T-shaped protrusion generally indicated byreference numeral 82. A complementary open channel 84 is similarlyconfigured in a T-shape to accept the T-shaped protrusion 82. Withreference to FIG. 23, it can be appreciated that other configurationsare suitable such as, but not limited to, a cylindrical configuration86, a dove-tail configuration 88, and a star shaped configuration 90. Itcan also be appreciated that, regardless of the configuration, variousfits can be used such as, but not limited to, an interference fit, ataper lock fit and a sliding fit secured by a mechanical fastener 60. Itcan further be appreciated that the mechanical fastener 60 can beinserted through an aperture and contact the T-shaped protrusion. Themechanical fastener can also connect to the T-shaped protrusion suchthat the fastener 60 can be inserted through a fastener aperture 92 inthe open channel and/or in the mounting location. It can be additionallyappreciated that the fastener can be placed at various angles andposition to further secure the components of the prosthesis.

It can be appreciated that the various components of the modularprosthesis can be scaled to fit the patients native bone structure. Acollar length 94 (FIG. 22) and a collar angle 96 (FIG. 24) can bevariable among multiple collar components 62, 68, while the collarmounting location 66 and the collar open channel 64 can have a fixeddimension to facilitate interchangeability among other stem components10 and head components 30. With reference to FIG. 20, it can also beappreciated that an inner core length 98 can vary such that the innercore body 22 can be completely contained within the head component innerhollow 34 or extend beyond an outer body shell aperture 100. It isfurther appreciated, that various dimensions such as length, diameter,thickness etc. can be varied to more closely match the native bonestructure of the patient, as shown in FIG. 14.

With reference to FIGS. 26A-26D, a threaded post 102 and a complementarythreaded aperture 104 can be used to connect the collar component 62 tothe head component 30 and the stem component 10. With reference to FIG.26A, the first connection portion 70 of the head component 30 caninclude the threaded aperture 104. The second connection portion 72 ofthe collar component 62 can include the threaded post 102 that canengage with and connect to the complimentary threaded aperture 104 onthe head component 30. The third connection portion 74 of the collarcomponent 62 can include the above described T-shaped protrusion 82. Thefourth connection portion 76 of the stem component 10 can include theabove described T-shaped channel 84, which can connect with the T-shapedprotrusion 82 included on the third connection portion 74 of the collarcomponent 62. It can be appreciated that the angled collar component 68(FIG. 26D) can be similarly configured to the collar component 62 (FIGS.26A-26C) and, thus, can be used interchangeably.

With reference to FIG. 26B, the first connection portion 70 on the headcomponent 30 can include the T-shaped protrusion 82. The secondconnection portion 72 of the collar component 62 can include thecomplimentary T-shaped channel 84 that can connect with and engage theT-shaped protrusion 82 included on the first connection portion 70 ofthe head component 30. The third connection portion 74 of the collarcomponent 62 can include the threaded post 102. The fourth connectionportion 76 of the stem component 10 can include the complementarythreaded aperture 104 that can engage to and connect with the threadedpost 102 included on the third connection portion 74 of the collarcomponent 62.

With reference to FIG. 26C, the first connection portion 70 of the headcomponent 30 can include the threaded aperture 104. The secondconnection portion 72 of the collar component 62 can include thethreaded post 102 which can engage with and connect to the threadedaperture 104 included on the first connection portion of the headcomponent 30. The third connection portion 74 of the collar component 62can also include the threaded post 102. The first connection portion 76on the stem component 10 can include the threaded aperture 104 that canengage with and connect to the threaded post 102 on the third connectionportion 74 of the collar component 62.

With reference to FIG. 26D, the first connection portion 70 of the headcomponent 30 can include the threaded aperture 104. The secondconnection portion 72 of the angle collar 68 can include the threadedpost 102, which can engage with and connect to the threaded aperture104. The third connection portion of the angle collar 68 can alsoinclude the threaded post 102. The fourth connection portion 76 of thestem component 10 can include the threaded aperture 104, which canengage with and connect to the threaded post 102. It can be appreciatedthat height 94 (FIG. 26C) and/or angle 96 of either the collar component62 or angled collar component 68 can be varied to accommodate the nativebone structure, as shown in FIG. 14. Moreover, the height 106 (FIG. 26C)of the threaded post 106 can be varied to further accommodate themodularity of the prosthesis. It can also be appreciated that the firstconnection portion 70, the second connection portion 72, the thirdconnection portion 74 and the fourth connection portion 76 can beconfigured in various ways including, but not limited to, the respectivethreaded posts 102 and threaded apertures 104 and various combinationsthereof.

With reference to FIG. 27, a kit 108 is shown including exemplary stemcomponents 10, collar components 62, angled collar components 68 andhead components 30. The kit 108 can include a collection of varioussizes and shapes of the above-mentioned components. For example, the kit108 can include a plurality of angled collar component 68 having varyingcollar angles 94. By way of further example, the kit 108 can include aplurality of head components 30 having varying shaped concave topportions 37 that complement the native bone to which they will contact.The kit 108 can also include a plurality of stem components 10 such thateach of the stem components 10 has varying size anchor portions 12 inthickness, taper design and/or length. Moreover, the kit 108 can includea plurality of collar components 62 having varying collar lengths 92 tofurther accommodate the native bone structure. It can be appreciatedthat the kit 108 can include numerous head components 30, angled collarcomponents 68, collar components 62, and stem components 10 of varioussizes, shapes and configurations so that the modular prosthesis systemcan be assembled to closely match the native bone structure.

The kit 108 provides the plurality of head components 30, angled collarcomponents 68, collar components 62, and stem components 10 that can beassembled and adjusted during a medical procedure to provide a fit thatcan be in-situ determined and adjusted. It can be appreciated that amedical professional can determine a proper length and angle and selectamong the components of the kit 108 to achieve the proper length andangle. Nevertheless, the medical professional can select and substitutecomponents in-situ to adjust to achieve the proper length and angle.

The description of the invention is merely exemplary in nature and,thus, variations that do not depart from the gist of the invention areintended to be within the scope of the invention. Such variations arenot to be regarded as a departure from the spirit and scope of theinvention. It is to be understood that the above-described arrangementsare only illustrative of the application of the principles of thepresent invention. Numerous modifications and alternative arrangementsmay be devised by those skilled in the art without departing from thespirit and scope of the present invention and the appended claims areintended to cover such modifications and arrangements. Thus, while thepresent invention has been shown in the drawings and fully describedabove with particularity and detail in connection with what is presentlydeemed to be the most practical and preferred embodiment(s) of theinvention, it will be apparent to those of ordinary skill in the artthat numerous modifications, including, but not limited to, variationsin size, materials, shape, form, function and manner of operation,assembly and use may be made, without departing from the principles andconcepts of the invention as set forth in the claims.

1. A prosthesis system for replacement of a head portion of a proximalradius, comprising: a monolithic stem component defining a stemanchoring portion having a stem longitudinal axis and configured tocouple to the proximal radius, and a dovetail-shaped first mountingportion extending along a mounting longitudinal axis transverse to thestem longitudinal axis; a head component having a dovetail-shaped secondmounting portion slidably engaged with the first mounting portion alongthe mounting longitudinal axis; and a locking mechanism formed by thestem component and the head component at an interface between the stemcomponent and the head component and movable from a disengaged state toan engaged state, wherein one of the first and second mounting portionsintersects the stem longitudinal axis and the locking mechanism isengaged through relative translational movement between the stemcomponent and the head component along the mounting longitudinal axis,the locking mechanism preventing relative movement between the stemcomponent and the head component in either direction along the mountinglongitudinal axis when moved from the disengaged state to the engagedstate.
 2. The prosthesis system of claim 1 wherein the locking mechanismincludes at least one elastically deformable protrusion movable from acompressed state permitting translational movement of the head componentrelative to the stem component along the mounting longitudinal axis toan expanded state restricting relative movement between the stemcomponent and the head component.
 3. The prosthesis system of claim 1wherein the locking mechanism is formed by a protrusion and acomplementary recess that define a pair of complementary faces thatengage in a direction perpendicular to the mounting longitudinal axiswhen the stem component and the head component are connected.
 4. Theprosthesis system of claim 3 wherein the protrusion is deformable. 5.The prosthesis system of claim 3 wherein the protrusion is formed on amounting surface defined by one of the first mounting portion and thesecond mounting portion.
 6. The prosthesis system of claim 3 wherein therecess is formed on a mounting surface defined by one of the firstmounting portion and the second mounting portion.
 7. The prosthesissystem of claim 1 wherein the locking mechanism is formed by a femaleconnection portion of the stem component and a male connection portionof a flange of the head component that engage along a directionperpendicular to the mounting longitudinal axis when the stem componentand the head component are connected.
 8. The prosthesis system of claim7 wherein the female connection portion and the male connection portionare brought into engagement through relative translational movementbetween the stem component and the head component along a single axis.9. The prosthesis system of claim 7 wherein the flange of the headcomponent is deformable.
 10. The prosthesis system of claim 1 whereinthe first and second mounting portions define a pair of complementarybearing surfaces and one of the pair of complementary bearing surfacesintersects the stem longitudinal axis.
 11. The prosthesis system ofclaim 10 wherein the one of the pair of complementary bearing surfacesintersects the stem longitudinal axis at an angle of 90 degrees.
 12. Theprosthesis system of claim 10 wherein the pair of complementary bearingsurfaces has an area of contact that intersects the stem longitudinalaxis.
 13. The prosthesis system of claim 1 wherein the first and secondmounting portions form an assembly plane that is normal to the stemlongitudinal axis.
 14. The prosthesis system of claim 1 wherein the headcomponent is a monolithic component.
 15. The prosthesis system of claim1 wherein the head component includes an articulating surface that isformed to slidably engage a native capitellum.
 16. A method of use for amodular prosthesis for replacement of a head portion of a proximalradius, comprising: coupling a stem anchoring portion of a monolithicstem component having a stem longitudinal axis to a resected portion ofthe proximal radius; and coupling a dovetail-shaped first mountingportion of a head component that extends along a mounting longitudinalaxis transverse to the stem longitudinal axis to a dovetail-shapedsecond mounting portion of the stem component that extends along themounting longitudinal axis, wherein coupling a dovetail-shaped firstmounting portion includes: slidably engaging the first mounting portionwith the second mounting portion; moving the head component along themounting longitudinal axis relative to the stem component; moving alocking mechanism from a disengaged state to an engaged state; andpreventing relative movement between the stem component and the headcomponent in either direction along the mounting longitudinal axis whenthe locking mechanism is in the engaged state.
 17. The method of claim16 wherein moving the locking mechanism from the disengaged state to theengaged state includes moving a projection of the locking mechanism in adirection perpendicular to the mounting longitudinal axis.
 18. Themethod of claim 16 further comprising determining in-situ a prostheticlength and selecting in-situ one of a plurality of head components, andone of a plurality of stem components to achieve a prosthetic length.